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Rapid development of electronic devices, ranging from personal communication devices to electric mobility solutions, has increased demand for energy storage devices not only in the production volume but also in the product functionality. Among many functional requirements including energy capacity, safety, and short recharge time, one of the major limitations is the short charging time while maintaining the designed capacity. However, even with the most updated lithium-ion battery (LIB) technology, it is well known that fast charging with a high current rate would reduce the lifetime of batteries significantly. Recently, among the many approaches to improve the quick charging performance, a pulse current charging method while keeping the total amount of energy has demonstrated a successful fast recharging of LIB without significantly degrading the battery capacity. The essence of the idea is to stop charging in the middle stage to provide a relaxation period instead of continuously charging at a high current rate. In this study, a comparative study between a conventional charging method with 3C current rate (equivalent to 20 min of charging time) and a pulse current charging with 6C current rate (10 min of charging and 10 min of relaxation time) was carried out. While the conventional charging method showed that the capacity was maintained up to about 200 cycles, the pulse current charging method revealed that the capacity was maintained for more than 450 cycles with a Coulombic efficiency of nearly 100%.
Seunghun Lee; Wonil Cho; Vandung Do; Woongchul Choi. Effects of Pulse Current Charging on the Aging Performance of Commercial Cylindrical Lithium Ion Batteries. Applied Sciences 2021, 11, 4918 .
AMA StyleSeunghun Lee, Wonil Cho, Vandung Do, Woongchul Choi. Effects of Pulse Current Charging on the Aging Performance of Commercial Cylindrical Lithium Ion Batteries. Applied Sciences. 2021; 11 (11):4918.
Chicago/Turabian StyleSeunghun Lee; Wonil Cho; Vandung Do; Woongchul Choi. 2021. "Effects of Pulse Current Charging on the Aging Performance of Commercial Cylindrical Lithium Ion Batteries." Applied Sciences 11, no. 11: 4918.
Due to rapid development of industries around the world, more and more consumption of fossil fuels was unavoidable, resulting in serious environmental problems. The many pollutant emissions—a major contributor to global warming and weather pattern change—have been at the center of concern. In order to solve this issue, research and development of electric vehicles and energy storage systems made great progress and successfully introduced products in the market. Nevertheless, accurate measurement of the state of charge (SOC) and state of health (SOH) of the Li-ion battery, the most popular electric energy storage device, has not yet been fully understood due to the nature of battery aging. In this study, ideas to estimate the capacity and ultimately SOC and SOH of Li-ion batteries are discussed. With these ideas, we expect not only to accommodate the issues with battery aging but also to implement an algorithm for an on-board battery management system. The key idea is to chase and monitor internal resistance continuously in a fast and reliable manner in real time. With further investigation of the key idea, we also fully expect to come up with a reliable SOC and SOH measurement scheme in the near future.
Woongchul Choi. A Study on State of Charge and State of Health Estimation in Consideration of Lithium-Ion Battery Aging. Sustainability 2020, 12, 10451 .
AMA StyleWoongchul Choi. A Study on State of Charge and State of Health Estimation in Consideration of Lithium-Ion Battery Aging. Sustainability. 2020; 12 (24):10451.
Chicago/Turabian StyleWoongchul Choi. 2020. "A Study on State of Charge and State of Health Estimation in Consideration of Lithium-Ion Battery Aging." Sustainability 12, no. 24: 10451.
While pollutant emissions from vehicles are under heavy scrutiny all around the world, small two-wheelers have not been under strict regulations until recently. Especially in the region of Southeast Asia, a tremendous number of old, in-house rebuilt and outdated two-wheelers are in operation and, as a result, pollutant emission problems are one of the most serious concerns of the communities. Since electric grid systems for consistent and stable supply of electricity are not there yet, thus plug-in series hybrid two-wheel vehicles have attracted much attention and are thought to be a meaningful solution for many people in the region. In the current study, an energy simulation tool has been developed to compare the ownership cost of an internal combustion engine (ICE)-based two-wheeler and that of a plug-in series hybrid electric scooter. To estimate annual energy cost (sum of gasoline and electricity cost), gasoline prices and household electricity rates in major Southeast Asian countries were collected. In addition, the nominal initial vehicle prices of ICE-based scooters and those of plug-in series hybrid electric two-wheel vehicles were gathered to estimate the time for the recovery of the initial investment.
Woongchul Choi; Seokho Yun. A Comparative Study of Initial Cost Recuperation Period of Plug-In Series Hybrid Electric Two-Wheel Vehicles in Southeast Asian Countries. Sustainability 2020, 12, 10340 .
AMA StyleWoongchul Choi, Seokho Yun. A Comparative Study of Initial Cost Recuperation Period of Plug-In Series Hybrid Electric Two-Wheel Vehicles in Southeast Asian Countries. Sustainability. 2020; 12 (24):10340.
Chicago/Turabian StyleWoongchul Choi; Seokho Yun. 2020. "A Comparative Study of Initial Cost Recuperation Period of Plug-In Series Hybrid Electric Two-Wheel Vehicles in Southeast Asian Countries." Sustainability 12, no. 24: 10340.
Global climate change is affecting human life more seriously than ever before. Countries around the world have identified cars as a significant source of pollution, leading to an increased interest in eco-friendly automobiles. Electric vehicles (EVs), which are characteristically eco-friendly, have become a choice for future transportation system. In this paper, we proposed a strategy for determining the appropriate placement of large-scale charging stations using K-mean algorithm. Also, the initial results were validated utilizing actual electricity usage data from the existing chargers. Currently in Korea, a typical public charging station has two to three chargers to support EV users. As EVs become more popular, new problems arise, such as charger hopping and/or long waiting lines. In order to address these new issues, a large-scale charging station concept which houses more than ten chargers, is suggested. In doing so, a strategic approach for selecting close-to-ideal locations for the charging stations is introduced to maximize the charging station’s effectiveness. In this study, Jeju Island, Korea, which has many EVs, was used as a testbed. With the wealth of EV chargers and their usage data, initial validation of the proposed methodology was made possible. During the evaluation of the best possible locations for the largescale charging stations, we considered the locations of tourist attractions and convenient support facilities, as well as the population. After the evaluations, the proposed locations were validated using actual long-term charger usage data on Jeju Island. The demonstrated strategy for identifying appropriate locations for large-scale charging stations can be used by other tourist heavy islands or even small countries.
Woongchul Choi. Placement of Charging Infrastructures for EVs using K-Mean Algorithm and its Validation using Real Usage Data. International Journal of Precision Engineering and Manufacturing-Green Technology 2020, 7, 875 -884.
AMA StyleWoongchul Choi. Placement of Charging Infrastructures for EVs using K-Mean Algorithm and its Validation using Real Usage Data. International Journal of Precision Engineering and Manufacturing-Green Technology. 2020; 7 (4):875-884.
Chicago/Turabian StyleWoongchul Choi. 2020. "Placement of Charging Infrastructures for EVs using K-Mean Algorithm and its Validation using Real Usage Data." International Journal of Precision Engineering and Manufacturing-Green Technology 7, no. 4: 875-884.
As part of the ongoing effort to be independent of petroleum resources and to be free from pollutant emission issues, various electric vehicles have been developed and tested through their integration with real world systems. In the current paper, yet another application specific EV for public transportation, an electric bus, is introduced and explained with results from the pilot test program which was carried out under real traffic conditions. The main feature of the current system is a battery exchanging mechanism mounted on the roof of the bus. The current configuration certainly requires an externally fabricated battery exchanging robot system that would complement the electric bus for a fully automated battery exchanging process. The major advantage of the current system is the quick re-charging of the electric energy through the physical battery exchange and the possible utilization of the battery exchange station as a mini scale energy storage system for grid system peak power shaving. With the total system solution approach for the public transportation system, it is fully expected to create outstanding business opportunities in number of areas such as battery suppliers, battery exchanging station management, battery leasing and many more.
Jeongyong Kim; Inho Song; Woongchul Choi. An Electric Bus with a Battery Exchange System. Energies 2015, 8, 6806 -6819.
AMA StyleJeongyong Kim, Inho Song, Woongchul Choi. An Electric Bus with a Battery Exchange System. Energies. 2015; 8 (7):6806-6819.
Chicago/Turabian StyleJeongyong Kim; Inho Song; Woongchul Choi. 2015. "An Electric Bus with a Battery Exchange System." Energies 8, no. 7: 6806-6819.
The demand for NOx after-treatment system has increased dramatically due to the stricter NOx emission regulations for diesel vehicles. The urea-SCR system is one of the NOx after-treatment methods found to be quite effective to meet the regulation requirement enforced by various authorities including the Euro-6. In order to develop an effective urea-SCR system, it is critical to establish an even distribution of reductant over the catalyst surface since this favorable distribution can increase reduction reaction and in turn, improve NOx conversion efficiencies. In the current study, a number of design variations of the urea-SCR system which included two mixer types and three decomposition pipe lengths, were evaluated systematically using CFD analysis and experimental measurements. The purpose of the CFD analysis was to estimate the distribution of reductant within the urea-SCR system with a specific configuration and the purpose of the engine emission test was to measure the amount of NOx reduction, respectively. The results from the systematic analysis revealed the relation between the reductant distribution over the SCR and the performance of the NOx reduction.
Y. S. Cho; S. W. Lee; W. C. Choi; Y. B. Yoon. Urea-SCR system optimization with various combinations of mixer types and decomposition pipe lengths. International Journal of Automotive Technology 2014, 15, 723 -731.
AMA StyleY. S. Cho, S. W. Lee, W. C. Choi, Y. B. Yoon. Urea-SCR system optimization with various combinations of mixer types and decomposition pipe lengths. International Journal of Automotive Technology. 2014; 15 (5):723-731.
Chicago/Turabian StyleY. S. Cho; S. W. Lee; W. C. Choi; Y. B. Yoon. 2014. "Urea-SCR system optimization with various combinations of mixer types and decomposition pipe lengths." International Journal of Automotive Technology 15, no. 5: 723-731.
In order to design a vehicle body with high strength and high stiffness, a multi-disciplinary design process should include careful consideration of multi-disciplinary design constraints to properly account for vehicle static stiffness (bending/torsional), durability, Noise/Vibration/Harshness (NVH), crash worthiness, light weight vehicle structure during the early stage of vehicle design process. With this approach, fast development of new vehicle body structures can be achieved with minimal number of iterations to match the conflicting design goals from each discipline. In the current research, a multi-disciplinary design optimization (MDO) based on a meta model is developed and refined to apply for the design of body structure. In an effort to apply the MDO for vehicle body structure, 4 phase procedures were established in the current research. In Phase I, a base model is created. In Phase II, an effect analysis is carried out. In Phase III, a meta model is created. Finally in Phase IV, using the optimization algorithm, the meta model created in Phase III is eventually refined through the process of optimization. In this research, static stiffness (bending / torsional), dynamic stiffness (1st torsion mode) were used for constrained conditions and the mass minimization was the object function for optimization.
S. J. Heo; In Hee Kim; D. O. Kang; W. Y. Ki; S. M. H. Darwish; Woo Chun Choi; Hyung Joon Yim. Multi-Disciplinary Constraint Design Optimization Based on Progressive Meta-Model Method for Vehicle Body Structure. Advanced Structured Materials 2013, 103 -115.
AMA StyleS. J. Heo, In Hee Kim, D. O. Kang, W. Y. Ki, S. M. H. Darwish, Woo Chun Choi, Hyung Joon Yim. Multi-Disciplinary Constraint Design Optimization Based on Progressive Meta-Model Method for Vehicle Body Structure. Advanced Structured Materials. 2013; ():103-115.
Chicago/Turabian StyleS. J. Heo; In Hee Kim; D. O. Kang; W. Y. Ki; S. M. H. Darwish; Woo Chun Choi; Hyung Joon Yim. 2013. "Multi-Disciplinary Constraint Design Optimization Based on Progressive Meta-Model Method for Vehicle Body Structure." Advanced Structured Materials , no. : 103-115.